Diisocyanate

ABSTRACT

A novel aliphatic diisocyanate, namely 1,4-bis(2-isocyanatoethyl)cyclohexane, is disclosed. Polyurethanes derived from this diisocyanate exhibit advantageous properties. Illustratively, polyurethane elastomers prepared from the above diisocyanate, a polymeric diol and a low molecular weight diol extender, possess significantly improved resilience properties and are useful in the preparation of automobile bumpers, fenders and the like.

This application is a division of application Ser. No. 440,565, filedNov. 10, 1982, and now U.S. Pat. No. 4,552,762.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to novel isocyanates and is more particularlyconcerned with novel aliphatic isocyanates and with methods for theirpreparation and with polyurethanes prepared therefrom by reaction withactive-hydrogen containing materials.

2. Description of the Prior Art

A wide variety is known of cyclohexanes substituted by isocyanatoalkylsubstituents. Illustratively U.S. Pat. No. 3,787,469 discloses1,4-bis(isocyanatomethyl)cyclohexane; U.S. Pat. No. 3,625,986 discloses1-(isocyanatomethyl)-1-(3-isocyanatopropyl)cyclohexane (see also U.S.Pat. Nos. 3,584,045 and 3,515,740) and1-(isocyanatomethyl)-1-(2-isocyanatoethyl)cyclohexane; U.S. Pat. No.3,624,122 discloses1-alkyl-2-isocyanatomethyl-4-isocyanatoalkylcyclohexanes; and U.S. Pat.No. 4,113,705 shows1-(2-isocyanatoethyl)-4-(isocyanatomethyl)-4-(3-isocyanatopropyl)cyclohexane.To the best of applicants' knowledge the compound1,4-bis(2-isocyanatoethyl)cyclohexane has not been described previously.It has now been found that this latter diisocyanate can be preparedreadily in high yield and that it can be utilized to preparepolyurethanes which possess highly advantageous properties.

SUMMARY OF THE INVENTION

This invention comprises a novel aliphatic diisocyanate, namely,1,4-bis(2-isocyanatoethyl)cyclohexane (I), and polyurethanes derivedtherefrom by reaction with active hydrogen-containing compounds inaccordance with processes well-known in the art.

DETAILED DESCRIPTION OF THE INVENTION

The novel aliphatic diisocyanate of the invention is preparedconveniently from the known compound 1,4-bis-(hydroxymethyl)cyclohexaneby the combination of steps shown schematically as follows: ##STR1##

In accordance with the above reaction scheme the starting diol (II) isreacted with phosgene, advantageously in the presence of an inertorganic solvent, to form the corresponding bis(chloroformate) usingprocedures well-known in the art; see, for example, S. Petersen, inHouben-Weyl, Methoden der Organischen Chemie, Vol. VIII, Part 3, p. 101,Georg Thieme Verlag, Stuttgart, 1952.

The term "inert organic solvent" means organic solvents which do notenter into reaction with any of the reactants employed in the process orinterfere in any other way with the desired course of the reaction.Illustrative of inert organic solvents are chloroform, dichloroethane,benzene, toluene, chlorobenzene and the like. The phosgenation isgenerally conducted at temperatures which, advantageously, are in therange of about 10° C. to about 120° C., and preferably in the range ofabout 60° C. to about 90° C. The progress of the reaction can befollowed by conventional analytical techniques such as infraredspectroscopy and the like. When the reaction is judged to be completethe bis(chloroformate) (III) can, if desired, be isolated from thereaction mixture, for example, by removing the inert organic solvent andany excess phosgene by distillation. However, it is generallyunnecessary to isolate the bis(chloroformate) (III) since it is foundthat the reaction product from the first step can, after purging anyexcess phosgene therefrom, be used as such in the next step of theprocess.

In the second step of the process the bis(chloroformate), advantageouslyin the form of the reaction mixture obtained in the first step, isheated in the presence of a catalytic amount of anN,N-disubstitutedformamide such as dimethylformamide, diethylformamideand the like using the process for the preparation of aliphatichydrocarbyl chlorides which is described in the application of ReinhardH. Richter et al Ser. No. 440,520 filed Nov. 10, 1982. The reaction isconducted at a temperature in range of about 40° C. to about 150° C. andpreferably in the range of about 60° C. to about 100° C. and thedecarboxylation of the bis(chloroformate) (III) to the corresponding1,4-bis(chloromethyl)cyclohexane (IV) proceeds smoothly and in highyield. The progress of the reaction can be followed by routineanalytical procedures such as infrared spectroscopic analysis or bymeasuring the amount of carbon dioxide eliminated from the reactionmixture. The compound (IV) can be isolated from the reaction mixture byany convenient means, if so desired. For example, the inert organicsolvent and the N,N-disubstitutedformamide catalyst can be removed bydistillation and the compound (IV) can, if desired, be purified bydistillation under reduced pressure or by chromatography or like means.Alternatively, for use in the next step of the process, the compound(IV) can be kept in solution in the reaction product and theN,N-disubstitutedformamide used as catalyst can be removed bydistillation or by extraction with water before proceeding to the nextstep of the process.

The bis(chloromethyl)cyclohexane (IV) obtained as described above isthen reacted in the presence of an inert organic solvent (the reactionsolution derived from the previous step without isolation of thecompound IV can be used) with an alkali metal cyanide such as sodium,potassium, lithium and the like cyanides using procedures well-known inthe art, such as described by R. A. Smiley and C. Arnold, J. Org. Chem.,25, 257, (1960) and L. Friedman and H. Shechter, J. Org. Chem., 25, 877,(1960). The reaction is conducted at temperatures in the range of about70° C. to about 180° C. and preferably about 80° C. to about 140° C.Advantageously, the alkali metal cyanide is added portionwise, withvigorous agitation, in the solid state to the solution of dichloride(IV) in the inert organic solvent. The reactants are employed in atleast stoichiometric proportions and advantageously with the alkalimetal cyanide present in slight excess over the stoichiometric amount.The reaction proceeds smoothly and gives the desired dinitrile (V) inhigh yield. The resulting reaction product is a mixture of alkali metalchloride (as a precipitate) and a solution of the dinitrile (V) in inertorganic solvent. The alkali metal chloride is removed by filtration,centrifugation and the like and the dinitrile (V) is isolated readily byevaporation of the solvent. The dinitrile (V) can be purified, ifdesired, by conventional techniques such as crystallization, beforebeing subjected to the next step in the process of the invention.

The dinitrile (V) is then hydrogenated to the corresponding diamine (VI)using any of the procedures known in the art for the reduction of anitrile to the corresponding amine; see, for example, Chemistry ofCarbon Compounds, edited by E. H. Rodd, Volume IIIA, p. 488, Elsevier,New York, 1954. Such techniques include reduction using sodium in thepresence of a lower aliphatic alcohol such as methanol, ethanol, and thelike as well as hydrogenation in the presence of a catalyst such assupported platinum and palladium catalysts, Raney nickel and the like.The diamine (VI) so obtained can be purified, if desired, byconventional procedures; for example, the diamine can be converted toits salt with a mineral or organic acid and the salt can be purified byrecrystallization before being converted back to the free diamine byreaction with the appropriate base such as an alkali metal hydroxide.

In the final step of the process the diamine (VI) is converted to thedesired diisocyanate (I) by phosgenation using procedures well-known inthe art. The phosgenation is carried out advantageously using proceduresdescribed by Siefken, Annalen, 562, 75 et seq., 1949. Illustratively,the diamine (VI) or an acid addition salt thereof such as thedihydrochloride, dihydrobromide, and the like, is treated with phosgenein the presence of an inert organic solvent such as benzene, toluene,anisole, xylene, naphthalene, decalin, chlorobenzene, dichlorobenzene,bromobenzene, chlorotoluene and the like. The reaction is conductedinitially at ambient or below ambient temperatures such as about -10° C.to about 20° C. and subsequently at elevated temperatures, preferably attemperatures of the order of 100° C. to 200° C. The phosgene isconveniently employed in approximately stoichiometric proportions but anexcess of phosgene can be employed if desired. The resultingdiisocyanate (I) is isolated from the reaction mixture by conventionalprocedures. For example, the excess phosgene is purged from the reactionmixture using a stream of nitrogen or other inert gas and the inertsolvent is removed by distillation under reduced pressure. The residualdiisocyanate (I) can be purified, if desired, by conventional proceduressuch as by distillation and the like.

The diisocyanate (I) is a colorless liquid. As will be readily apparentthe diisocyanate (I) can exist in a number of stereoisomeric forms.While theoretically more than two stereoisomeric forms are possible, itis found in practice that the cyclohexane ring tends to assume the"chair" configuration rather than the "boat" configuration at least atroom temperature and that, with the cyclohexane ring in the "chair"form, the two stereoisomers present in the diisocyanate (I) are the cis-and the trans-isomer. The above two isomers in the diisocyanate (I) canvary in proportion depending principally on the proportion of theseisomers present in the starting diol (II) unless specific steps aretaken to separate the two isomers or enhance the proportion of oneisomer with respect to the other at some stage in the conversion of thestarting diol (II) to the diisocyanate (I). If desired, thestereoisomers can be separated by known procedures, such as fractionalcrystallization or distillation or after derivatization, i.e. conversionof (VI) into a bis(imine) followed by fractional crystallization.

Thus, the diisocyanate (I) can be prepared in the form of the puretrans-isomer or the pure cis-isomer or a mixture of these two isomers inany proportion. Depending upon the particular use for which thediisocyanate (I) is to be employed it may be important to select aparticular isomer or mixture of isomers as discussed in more detailbelow. However, it is to be understood that any and all such isomers andmixtures of isomers are included within the present invention.

The diisocyanate (I) can be employed in the preparation ofpolyurethanes, both cellular and non-cellular, which have hitherto beenprepared from closely related aliphatic diisocyanates. In common withthe known aliphatic isocyanates the diisocyanate (I) of the inventiongives rise to polyurethanes which do not suffer discoloration on aging,i.e. do not give rise to the brown color which is a characteristic ofaged polyurethanes prepared from aromatic polyisocyanates. This propertymakes the diisocyanate (I) advantageous in the preparation ofpolyurethanes for coating compositions which are water-white,transparent and resistant to color formation on aging. The diisocyanate(I) is also highly advantageous in the preparation of elastomers whichare generally prepared by reaction with polymeric diols and lowmolecular weight extender diols in accordance with methods well-known inthe art. It is found that the elastomers so prepared exhibitsignificantly improved resilience properties (as measured by ASTM-D2632test for resilience) when compared with elastomers prepared in exactlythe same manner using the next lower homologue, namely1,4-bis(isocyanatomethyl)cyclohexane, of the diisocyanate (I); see thedata set forth in Example 2 below. In this type of application theproportion of stereoisomers in the diisocyanate (I) plays a role. Thusthe properties, particularly the resilience, of the elastomers inquestion is enhanced to the greatest extent when the pure trans-isomeris employed and, when a mixture of stereoisomers is used, the degree ofenhancement of properties is substantially directly proportional to theproportion of trans-isomer present in the starting diisocyanate.

The following examples describe the manner and process of making andusing the invention and set forth the best mode contemplated by theinventors of carrying out the invention but are not to be construed aslimiting.

EXAMPLE 1 A. Preparation of 1,4-bis(chloromethyl)cyclohexane (IV).

A charge of 250 ml. of 1,2-dichloroethane was heated under reflux whilea stream of phosgene was bubbled into the liquid and a total of 58 g.(0.4 mole) of 1,4-bis-(hydroxymethyl)cyclohexane was added in smallportions over a period of 1 hour, allowing the material added in eachportion to dissolve before the next portion was added. Shortly after theaddition was completed, the introduction of phosgene was terminated andthe excess phosgene was purged from the reaction mixture using a streamof nitrogen. When the purging was complete, part of the dichloroethanesolvent was removed by evaporation. To the concentrate was added 10 ml.(0.13 mole) of dimethylformamide and the resulting mixture was heatedunder reflux for approximately eight hours. At the end of this time theexcess solvent and dimethylformamide were removed by distillation underlow vacuum and the residue was distilled in vacuo to obtain 66.93 g. (92percent theoretical yield) of 1,4-bis(chloromethyl)cyclohexane in theform of a colorless liquid having a boiling point of 65° to 70° C. at0.1 mm. of mercury.

B. Preparation of 1,4-bis(cyanomethyl)cyclohexane (V).

A suspension of 70 g. (1.4 mole) of sodium cyanide in 200 ml. ofdimethyl sulfoxide was heated with stirring to 90° C. and a total of108.6 g. (0.6 mole) of 1,4-bis-(chloromethyl)cyclohexane was added overa period of approximately 1 hour. The temperature of the reactionmixture reached a maximum of 168° C. shortly after addition commencedbut levelled off at 130°-132° C. towards the end of the addition. Afterthe addition was complete, the resulting mixture was maintained at 115°C. with continuous stirring for a further 1.5 hr. and was then cooled toroom temperature (circa 20° C.). The cooled mixture was filtered and theinsoluble material was washed on the filter with dimethyl sulfoxide. Thecombined filtrate and washings were distilled to remove the majorportion of the solvent and the undistilled residue was allowed to coolto room temperature whereupon it crystallized. The residue was dissolvedin 200 ml. of toluene and the solution so obtained was extracted 5 timeswith 40 ml. portions of water to remove the last traces of dimethylsulfoxide. The washed toluene solution was dried over anhydrous sodiumsulfate and the toluene was then removed by distillation. The residuecrystallized in the form of a honey-colored solid. There was thusobtained 92.5 g. (94 percent theoretical yield) of1,4-bis(cyanomethyl)cyclohexane. The identity and purity of the productwas confirmed by gel permeation chromatography and by infrared andnuclear magnetic resonance spectra.

C. Preparation of 1,4-bis(2-aminoethyl)cyclohexane (VI).

A total of 50 g. of 1,4-bis(cyanomethyl)cyclohexane (prepared asdescribed above), 100 ml. of toluene, and 8 g. of Raney nickel(previously washed with methanol and toluene) was charged to a Parr bombhydrogenation apparatus. The bomb was cooled in dry ice and pressuredwith anhydrous ammonia followed by hydrogen to a pressure of 800 psi.The bomb was then heated to 90°-100° C. at which point the pressurereached 1040 psi. After about 1 hour of heating the uptake of hydrogenbegan. When the pressure had fallen to 400 psi the bomb was charged withadditional hydrogen to a pressure of 820 psi. The pressure fell to 500psi over a period of 2.75 hours and the bomb was again repressured to800 psi and hydrogenation was continued for a further 1 hour at the endof which time the pressure had fallen to 770 psi. The hydrogenation wasthen stopped and the reaction product was cooled to room temperature(circa 20° C.) and allowed to stand overnight. The reaction product wasthen filtered and the insoluble material was washed on the filter withtoluene. The combined filtrate and washings were then distilled underreduced pressure to remove the toluene and the residue was distilled invacuo to yield 48.8 g. (93 percent theoretical yield) of1,4-bis(2-aminoethyl)cyclohexane (VI) in the form of an oil having aboiling point of 86°-92° C. at 0.1 mm. of mercury. This diamine wasshown by C-13 nuclear magnetic resonance spectral analysis to containthe cis- to trans-isomers of (VI) in a ratio of approximately 1:2.5.

D. Preparation of 1,4-bis(2-isocyanatoethyl)cyclohexane (I).

A total of 160 g. (1.62 mole) of phosgene was dissolved in 400 ml. ofanisole maintained in a cooling bath at 8°-10° C. The resulting solutionwas maintained at the same temperature and stirred while a solution of48 g. (0.28 mole) of 1,4-bis(2-aminoethyl)cyclohexane (prepared asdescribed above) in 275 ml. of anisole was added dropwise under anatmosphere of nitrogen. The addition took place in 1 hour and 10minutes. After the addition was complete, the resulting mixture washeated gradually to 112°-115° C. and finally to a temperature of 131° to135° C. over a total time of 5 hours. During the heating period a streamof phosgene was bubbled through the reaction mixture. At the end of theheating period the reaction mixture was purged of excess phosgene usinga stream of nitrogen and was then evaporated on a rotary evaporator toremove the bulk of the solvent. The remainder of the solvent was removedby distillation and the residue was distilled under reduced pressure toobtain 54.6 g. (87 percent theoretical yield) of1,4-bis-(2-isocyanatoethyl)cyclohexane in the form of an oil having aboiling point of 130°-133° C. at 0.1 mm. of mercury. The material wasfound to have an isocyanate equivalent of 113. The identity of thematerial was confirmed by the infrared spectrum and the nuclear magneticresonance spectrum.

EXAMPLE 2

This example shows a direct comparison of two elastomers made underidentical conditions and using the same reactants in the sameproportions by equivalents, the sole difference being that in one casethe isocyanate used was 1,4-bis(2-isocyanatoethyl)cyclohexane and, inthe other case, was 1,4-bis(isocyanatomethyl)cyclohexane. The latterdiisocyanate was prepared from the corresponding diamine (Eastman Kodak)by phosgenation using the same procedure as that described in Example 1,Part D. The starting diamine was found to have a ratio of content ofcis- to trans-isomer of 1:3.3; i.e. the1,4-bis(isocyanatomethyl)cyclohexane derived therefrom had asignificantly greater trans-isomer content than the diisocyanate ofExample 1 above.

The procedure employed to prepare both elastomers was as follows. Thereactants and proportions (by equivalents or by weight where indicated)of each were:

    ______________________________________                                                            Proportion                                                ______________________________________                                        Polytetramethylene glycol                                                                           1.0 equivs.                                             Eq. wt. = 488.7 (Teracol 1000:DuPont)                                         1,4-butanediol        2.25 equivs.                                            Diisocyanate          3.25 × 1.02 (index)                               Antioxidant (Irganox 1010)                                                                          0.25% w/w*                                              Lubricant (Advawax 280)                                                                             0.5% w/w*                                               Catalyst (50% solution of stannous                                                                  0.025% w/w*                                             octoate in dioctyl phthalate)                                                 ______________________________________                                         *Proportions based on total weight of reactants.                         

The polytetramethylene glycol, 1,4-butanediol, anti-oxidant, catalystand lubricant were mixed and the mixture was degassed by heating at 90°to 100° C. for 2 hours at a pressure of about 0.1 mm. of mercury. Thediisocyanate was added to the degassed mixture with vigorous stirringand the mixed reactants were poured into a Teflon lined pan and reactionwas allowed to proceed to completion. The resulting polyurethane wasthen granulated, dried at 90° C. for 4 hrs. and subjected to injectionmolding using a barrel temperature of 200° to 210° C. and a moldtemperature of 50° C., to form test sheets (43/4"×43/4"×1/16") fordetermination of physical properties. The physical properties sodetermined for the two elastomers were as follows.

    ______________________________________                                                    Elastomer from                                                                             Elastomer from                                                   1,4-bis(isocyanato-                                                                        diisocyanate of                                                  methyl)cyclohexane                                                                         Example 1                                            ______________________________________                                        Tensile strength: psi                                                                       4700           2550.sup.1                                       Elongation at break: %                                                                       630           840                                              Hardness: Shore A                                                                            93             91                                              Clashberg Modulus T.sub.c                                                                   -64° C. -66° C.                                   Bayshore rebound                                                                             29             35                                              (ASTM-D2632)                                                                  Density g/cc  1.094          1.084                                            ______________________________________                                         Footnote:                                                                     .sup.1 The test bars showed "necking", i.e. stretching at approximately       the midpoint rather than uniformly throughout the bar.                   

The above results demonstrate that the elastomer prepared from thediisocyanate of Example 1 possessed significantly superior elongationand resiliency as compared with the elastomer from the prior artdiisocyanate in spite of the higher trans-isomer content of the latter.The higher trans content would be expected to enhance the resiliency ofthe elastomer. The difference in resiliency as measured by the abovetest confirmed an observation made in a simple manual test in which itwas observed that the elastomer prepared from the diisocyanate ofExample 1 had a much "snappier" feel, i.e. upon flexing the test sheetof the elastomer the return to original configuration upon release wasvery rapid in the case of the elastomer prepared from the diisocyanateof Example 1 but much more sluggish in the case of the elastomerprepared from the prior art diisocyanate.

We claim:
 1. In a polyurethane elastomer prepared by the reaction of anorganic diisocyanate, a polymeric diol and a low molecular weight diolextender the improvement which comprises employing1,4-bis(2-isocyanatoethyl)cyclohexane as the organic diisocyanate.
 2. Apolyurethane elastomer according to claim 1 wherein the1,4-bis(2-isocyanatoethyl)cyclohexane is present as the cis-isomer, thetrans-isomer, or mixtures of the two isomers in any proportion.